1. Field of the Invention
This invention relates generally to patterned-media magnetic recording disks, wherein each data bit is stored in a magnetically isolated data island on the disk, and more particularly to a patterned-media disk with patterned nondata islands for head-positioning and data synchronization.
2. Description of the Related Art
Magnetic recording hard disk drives with patterned magnetic recording media have been proposed to increase the data density. In patterned media, the magnetic recording layer on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional continuous media wherein a single “bit” may have multiple magnetic domains separated by domain walls. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. In one type of patterned media, as described for example in U.S. Pat. No. 6,440,520, the islands are elevated regions or pillars that extend above the spaces and magnetic material covers both the islands and the spaces, but the spaces are far enough from the read/write head to not adversely affect reading or writing, so the spaces can be considered essentially nonmagnetic. Alternatively, the patterned media may be fabricated so that that there is no magnetic material in the spaces between the islands. U.S. Pat. Nos. 5,820,769; 5,587,223; and 6,383,598 are representative of various types of patterned media and their methods of fabrication.
Like conventional non-patterned or continuous-media disks, patterned-media disks also have nondata regions that are used for read/write head positioning and data synchronization. The nondata regions in patterned-media disks contain nondata islands separated by nonmagnetic spaces. The proposed method for formatting this type of disk is to DC “erase” the disk during manufacturing with a large magnet, leaving all of the nondata islands magnetized in the same direction. Thus for a patterned-media perpendicular magnetic recording disk, all of the nondata islands would have a magnetization direction either “into” or “out of” the surface of the disk. However, because only a single polarity of magnetization is used with this method, half of the available signal amplitude from the nondata islands is sacrificed and thus the signal-to-noise ratio (SNR) is less than optimum.
What is needed is a patterned-media magnetic recording disk with nondata islands that have alternating polarity of magnetization to provide optimal SNR, and a relatively fast and low-cost method for formatting the disk.